PROTOZOA AND OTHER ANIMALS 913 



From this survey of the distribution of members of the genus Hex- 

 amita, it is apparent that the flagellates are as widespread in animals as are 

 members of the strictly endozoic genus Trichomonas. In their case, how- 

 ever, flagellates equally or more closely related than most of the endozoic 

 forms to the ancestral type are common free-living forms. The endozoic 

 forms, nevertheless, are for the most part as strictly adapted to their 

 habitat as trichomonads. 



There is no evidence, except possibly in certain species in Amphibia 

 and invertebrates, that the obligate symbionts have been recently adapted 

 from facultatively endozoic forms; any more than that Trichomonas can 

 be supposed to have recently so originated. There is little evidence of 

 parallelism in phylogenetic development in members of these two 

 genera and their hosts (Wenrich, 1935). 



In most instances Hexa?nita has been regarded as a commensal in its 

 hosts. A possible exception in an invertebrate host is Hexamita tubifci. 

 In the body cavity of the aquatic annelid the flagellates may be fatal to 

 the host, in a manner comparable to the effect of Glaucoma in dipteran 

 larvae and Astasia in Chaetogaster. Hinshaw, McNeil, and Kofoid 

 (1938b), on the basis of experimental data which they obtained, sug- 

 gested a possible relationship between a condition of enteritis in young 

 turkeys and a heavy infection of Hexamita that occurred in the affected 

 part of the small intestine. They also reviewed reports of possible rela- 

 tionship in other vertebrates between pathological conditions and the 

 occurrence of Hexamita. 



HOLOTRICHA 



Among holotrichous ciliates, all types of biotic relationship exist, so 

 that the group is especially favorable for study of the development of 

 symbiosis and host-specificity. In this section will be considered holotrich 

 groups in which free-living and symbiotic species are closely related. 



In some instances it seems that there has been no more than survival 

 of ordinarily free-living forms in or on a host, where certain conditions 

 of nutrition or protection favored the occurrence of the associate. Per- 

 haps the occurrence of Coleps hirtus on the rhabdocoele Vortex sexden- 

 tatus as a common epizo5n, as recorded by Graff (1882), is a relation- 

 ship of this type. 



The relationship of Enchelys dif^ugiarum Penard to Difflugia acumi- 



